REGIONS

Urban Air Quality Improved By Specific Type Of Trees

27 October 2010

Some trees are better than others at improving the air quality of our towns and cities according to an environmental expert in his new book, "The Development of an Urban Tree Air Quality Score (UTAQS): using the West Midlands, UK Conurbation as a Case Study Area".

Rossa Donovan, environmental scientist for international consultancy WYG, has investigated the feasibility of using trees to improve urban air quality and has discovered that of the 30 species considered, Scots pine, European larch and silver birch have the greatest ability to improve air quality, whilst oaks, willows and poplars can worsen air quality if planted in very large numbers.

Model scenarios were used to develop an Urban Tree Air Quality Score (UTAQS) that ranks trees in order of their ability to improve air quality. The UTAQS classification is applicable to all urban areas of the UK and other mid-latitude, temperate climate zones with common species to the UK.

Rossa Donovan, Regional Director, WYG commented: “This book contributes to the growing body of academic research that seeks to understand the importance of ecosystem services in our towns and cities. Many of us are aware of the important role that trees play in carbon sequestration and oxygen production but their other benefits (and costs) to society are less well known.

Trees enhance the aesthetics of our built environment, provide shade and wind shelter to our homes and workplaces, they also slow down the run-off of rain from urban catchments, thus reducing flood risk.

Although trees play an important role in improving urban air quality by filtering particulate pollutants from the air, they can also negatively impact the air quality of urban atmospheres. Chemicals that are released by trees as a by-product of photosynthesis can react with traffic fumes to cause photochemical smog and air-borne particles. The rate at which these smog and particle inducing chemicals are released depends on the species of tree and the environmental conditions at the time. Poor air quality can affect the health of people who live in cities leading to a number of chronic and acute medical conditions. The study presented in this book has, for the first time in the UK, attempted to rank the importance of 30 of the most common tree species found in urban areas in terms of their ability to positively or negatively affect the air quality of urban areas.”

Rossa, who is responsible for the delivery of WYG’s ecological services nationally, has 20 years of experience in ecology and arboriculture and is supported by a team of thirty-plus trained and experienced ecologists. He is also an expert panel and steering group member for the Engineering and Physical Sciences Research Council (EPSRC) Sustainable Urban Futures programme, where he gives advice on aspects of ecology and sustainability.

Rossa continued: “The research used data collected from a random, stratified survey of trees in the West Midlands to provide data on the physical attributes of its urban forest. The data were then fed into an atmospheric chemistry model which was used to model the combined effects of pollutant deposition to and the emission of biogenic volatile organic compounds (BVOCs) from the urban forest. By running different model scenarios we were able to virtually manipulate the tree composition of the West Midlands urban forest and thus determine the impact of individual species on urban air quality. By analysing the results of these model runs we were then able to group trees into those that have the greatest potential to improve air quality, those which have a fairly benign or moderate impact on air quality and those which would have a detrimental impact on air quality if planted in very large numbers.”

The study shows that it is possible to assess the positive and negative impacts that urban trees have on air quality and create an end-user tool that can be used by urban planners, architects, engineers and local authority officers to enhance the environment in their areas.

Improving air quality is only one of the many ecosystem services that the natural environment can provide society. Rossa believes that with further research it should be possible to quantify other benefits provided by, and the costs associated with, natural features and ultimately the contribution that they make to our economy.

Others that contributed to the book were, Sue Owen an Environmental Scientist at CEH, Edinburgh, Hope Brett an Environmental Scientist at the EA, Rob MacKenzie a Reader of Atmospheric Chemistry and Nick Hewitt Professor of Atmospheric Chemistry both at the Lancaster Environment Centre, Lancaster University.

The Development of an Urban Tree Air Quality Score (UTAQS): using the West Midlands, UK Conurbation as a Case Study Area is available on Amazon and in all large bookstores across the UK.